Reactor and Process For At Least Partially Decomposing and/or Cleaning Plastic Material

ABSTRACT

A reactor for gasifying and/or cleaning, in particular for depolymerizing, plastic material ( 12 ) with a reactor tank ( 14 ) for receiving the plastic material ( 12 ), wherein the reactor tank comprises a metal melt, a heating system ( 18 ) for heating the plastic material ( 12 ) in the reactor tank ( 14 ). According to the invention, a guide apparatus ( 24 ) arranged in an internal space ( 22 ) of the reactor tank ( 14 ) is provided for guiding liquefied plastic material ( 12 ) in the reactor tank ( 14 ), wherein the guide apparatus ( 24 ) is intended to guide the liquefied plastic material ( 12 ) on a helical path.

The invention refers to a reactor for gasifying and/or cleaning according to the generic term in claim 1. According to a second aspect the invention refers to a process for at least partially decomposing, in particular for depolymerizing, and/or cleaning plastic material.

Used plastic items are currently recycled mostly by processing them to create products for which the quality of the plastic material is not so important, for example benches or poles. However, using them in this way does not allow for the disposal of the immense amounts of plastic waste, so that a large proportion of the plastic waste is used as fuel.

An apparatus for treating waste according to the preamble of claim 1 is described in U.S. Pat. No. 5,436,210 wherein the waste is introduced from below into a bath of liquid metal. The waste decomposes and leaves the bath in the form of a liquid or a gas.

An apparatus is described in EP 1 840 191 A1 for gasifying biomass. A reactor of this sort is generally not suitable for gasifying or cleaning plastic material, as the underlying chemical processes are different.

A thermal decomposition apparatus is described in JP 2004 256 773 wherein the item to be pyrolized is guided into a horizontally running pipe, which is heated from outside. In order to remove residues, the decomposition apparatus comprises a rotating screw by means of which the residues are pushed towards a pipe end, where they are removed.

The invention aims to propose a reactor for gasifying and/or cleaning plastic material that only requires a small space.

The invention solves the problem by means of a reactor according to the preamble of claim 1 whose guide apparatus is designed to guide the liquefied plastic material on a helical path.

According to a second aspect, the invention solves the problem by means of a process for at least partially decomposing, in particular depolymerizing, and/or cleaning plastic material with the steps: (a) introducing the plastic material into a reactor tank that stretches along a longitudinal axis, (b) heating the plastic material by means of a heating system and (c) guiding the plastic material on a path about the longitudinal axis of the reactor tank by means of a guide apparatus which is arranged in an internal space of the reactor tank.

The advantage of the invention is that the plastic material in the reactor covers a long path, meaning that a large proportion of it reacts chemically. By guiding the plastic material on the helical path, the reactor can be built to be very compact, which reduces the loss of heat through radiation.

Within the scope of the above description, the term reactor can be understood to mean in particular a thermocatalytic depolymerization reactor. This refers to a reactor that is designed to thermally and/or catalytically depolymerize supplied polymers and/or to decompose them into materials with a low melting or boiling point. However, the reactor can also be designed for cleaning plastic material. The temperature in the reactor is then preferably selected in such a way that the contaminant is decomposed, but the plastic material remains uninfluenced.

The term heating system should be understood to mean every apparatus that is intended to supply heat energy to the plastic material inside the reactor tank. It preferably refers to an inductive heating system which generates heat inductively, at least in parts of the reactor tank and/or in components arranged in the internal space of the reactor tank. This has the advantage that parts located a long way radially into the reactor tank can also be heated efficiently.

The term guide apparatus should be understood to mean in particular a structure that is designed in such a way that each conceived volume element of the plastic material must go round the longitudinal axis at least once. Of course, this only applies to the components of the conceived volume element that have not been converted into gas. In particular, the guide apparatus is intended to be flat. For example, the guide apparatus may be made from a metal sheet.

The property that the guide apparatus is designed to guide the liquefied plastic material on a helical path may be understood particularly to mean that the guide apparatus is designed in such a way that it forces the liquefied plastic material onto a path which runs at least twice, but particularly several times, around the longitudinal axis of the reactor tank. It is possible, but not necessary, for the guide apparatus to be helical. For example, it is also possible that the guide apparatus is made up of a number of metal sheets that run largely horizontally in some sections and diagonally upwards in other sections. In this case, the plastic material flows on a path that runs upwards only in some sections and runs largely horizontally in other sections.

The reactor preferably comprises a supply apparatus for supplying plastic material. This supply apparatus is preferably arranged close to the base of the reactor tank. It may comprise an extruder by means of which the plastic material can be plasticized.

According to the invention, the reactor tank comprises a metal melt. The metal melt can, for example, comprise a Wood's metal. In general it is advantageous of the metal melt has a maximum melting point of 300° C.

It is favorable if the reactor comprises a condenser by means of which gases leaving the reactor tank can be condensed. Gases of this sort are mostly products of the decomposition of the plastic material. It is favorable if the reactor tank comprises plastic material in the form of polyolefin, which is introduced into the reactor tank from below via the dosing apparatus, for example. Should the polyolefin decompose, an oil-like substance is formed which can be burnt to create heat or used for synthesis purposes.

According to a preferred embodiment, the guide apparatus runs upwards with an increasing radial distance, relative to a vertical cross section. In other words, the guide apparatus is designed in such a way that the plastic material striking the guide apparatus is guided upwards and to the radial outside. In this case, gas resulting from the decomposition of the plastic material collects, preferably on the radial outer edge of the guide apparatus.

Alternatively it is possible for the guide apparatus to run horizontally, relative to a vertical cross section, or downwards, with an increasing radial distance. In this case, it is favorable if the reactor comprises a central column, so that plastic material which has been guided inside cannot flow above the radial inner edge of the guide apparatus and rise directly upwards.

It is also possible for the guide apparatus to run horizontally in some sections, relative to a vertical axis, upwards in other sections with a decreasing radial distance, and/or upwards in other sections with an increasing radial distance. In this way, the flow of the resulting gas can be influenced at will.

According to a preferred embodiment, the guide apparatus is constructed from ferromagnetic material in at least some sections. This is particularly favorable if the heating system is an inductive heating system. The guide apparatus is then heated by the alternating electromagnetic field emitted by the inductive heating system, so that the temperature in the direct vicinity of the guide apparatus is particularly high. It is favorable if the thickness of the guide apparatus has a value of at least 1 millimeter, in order to ensure a sufficient mechanical stability on the one hand, and on the other hand, to achieve a good connection to the inductive alternating field.

The guide apparatus preferably has recesses which run continuously from bottom to top. These recesses can be bore holes, slots or gaps between the recess and, for example, an inner side of the reactor tank.

Furthermore, it is favorable if the recesses are arranged at least marginally, in particular radially outwards and/or radially inwards. Here, it is favorable if the recesses have a small cross section or a small clear width. This leads to an especially high flow resistance against liquid plastic material.

According to a preferred embodiment, the guide apparatus comprises a thickening adjacent to at least one part of the recesses. This may be understood to mean that the guide apparatus is designed in such a way that one of the surfaces facing the recess is larger than a thickness of the guide apparatus would be at the same point without this thickening. In particular this thickening is constructed from ferroelectric material. For example, the guide apparatus may comprise a metal sheet in which the recesses can be made. Thickening elements can then be welded to the recesses, for example.

In order to improve the energy transfer from the alternating magnetic field, it can preferably be planned for the reactor tank to comprise ferroelectric material at least on the side facing the inner space, or to be made from ferroelectric material.

In addition, it is favorable if the reactor comprises heating elements in its inner space, which may comprise ferroelectric material. These heating elements may refer to balls, for example. It is generally favorable if the heating elements are convex, wherein a conceived enclosing sphere has a minimum diameter which surrounds the heating element, in particular a diameter of 50 millimeters at the very most. In addition, it is favorable if this enclosing sphere diameter has a value of at least 3 millimeters.

With the aid of a drawing an embodiment of the present invention will be explained in more detail. What is shown is:

FIG. 1 a reactor according to the invention for carrying out a method according to the invention.

FIG. 1 shows a reactor 10 according to the invention for gasifying plastic material 12, in particular polyolefin polymers. The reactor comprises a reactor tank 14 for heating the plastic material 12, which is introduced through the base into the reactor tank 14 via an extruder 16, for example.

The reactor 10 comprises a heating system 18 in the form of an inductive heating system which has a number of coils 20.1, 20.2, . . . , 20.5 by means of which an alternating magnetic field is generated in an inner space 22 of the reactor tank 14. The coils 20 (references without a numerical suffix refer to the item in general) are connected to a power supply unit, not depicted here, which creates an alternating current in the coils. The frequency of the alternating current lies, for example, within a range from 25 to 50 kHz. Higher frequencies are possible, but they lead to an increase in the so-called skin effect, which is not desirable.

A guide apparatus 24 is arranged in the inner space 22 of the reactor tank 14, by means of which the plastic material 12 is guided on a helical path around a longitudinal axis of the reactor tank 14. In the present case the guide apparatus is designed as a screw.

The reactor tank 14 is filled with a metal melt 26, which has a maximum melting point of T_(melt)=300° C. For example, the metal melt is made from Wood's metal. As a rule, the metal melt has a density of more than 9 grams per cubic centimetre, thereby giving a lift to the plastic material 12 and pressing it from below onto the guide apparatus 24.

Due to the temperature T in the reactor tank 14 the plastic material 12 decomposes gradually, creating gas bubbles 28.1, 28.2, . . . in the process. The metal melt 26 can have a catalytic effect on the decomposition process, meaning that the reactor 10 can refer to a thermocatalytic depolymerisation reactor. In particular, the plastic material refers to polyolefin, which depolymerises under the influence of temperature, so that the gas bubbles 28 may contain alkanes, alkenes and alkynes.

The screw shape of the guide apparatus 24 means that the plastic material 12 moves upwards along its path from one entrance opening 20, which is preferably arranged on the base of the reactor tank 14, on a helical path, i.e. on a path that winds around the longitudinal axis L. A current direction of the flow of the plastic material 12 thus points upwards in vectorial notation and has a large circumferential component, which is larger than a radial component.

FIG. 1 shows the reactor 10 in a vertical cross section. It should be recognised that the guide apparatus 24 runs downwards with an increasing radial distance r from the longitudinal axis L relative to this cross section. As a result, plastic material 12 striking the guide apparatus 24 is guided to the radial inside. In particular, the gas bubbles 28 move to the radial inside, where they hit a column 32. The guide apparatus 24 comprises a number of recesses 34.1, 34.2, . . . , through which gas can easily escape upwards.

As the partial diagram in FIG. 1 shows, thickenings 36.1, 36.2 are arranged directly on the recesses 34, such as 34.3, the thickenings being made from welded iron bars in the present case. As iron is a ferromagnetic material, the thickenings 36 heat up: a gas bubble 28.3 passing through the recess 34.3 is also heated in the same way as any plastic material passing through. The thickening 36 thus has the effect that a surface A facing away from the recess 34.3 is larger than a surface A′, which would face away from the recess 34.3 if the thickening 36 were not available. In other words, the thickening 36 leads to an increase in the local thickness D.

FIG. 1 schematically depicts that a recess 34.4 in the form of a continuous slot can be arranged on an inner edge 38 of the guide apparatus 24, located on the radial inside. As the highest point is located on the radial inside relative to a winding in the screw, gas can be discharged upwards particularly effectively through this recess which is located on the radial inside.

The reactor tank 14 is constructed from a ferromagnetic material on the side facing the inner space 22, for example from iron or magnetic steel. Furthermore, the guide apparatus 24 is also made from ferromagnetic material, so that they are heated by the induction heating system 18. The induction heating system 18 is designed in such a way that a temperature gradient occurs wherein the temperature rises with an increase in height. At the lower end of the reactor tank 14, the temperature generally has an value of approximately T=300° C., whereas in the upper area, it is around T=450° C.

The reactor 10 has a pollutant remover 40, which is arranged at the upper end of the reactor tank 14. As typical pollutants from plastic material, such as sand, are lighter than the metal bath, they float on top and can be removed from above. The reactor 10 also comprises a gas vent 42 that flows into a condenser 44 and any occurring gas is removed. Liquid material leaving the condenser 44 ends up in a collector 46.

A process according to the invention is carried out by pre-heating the plastic material 12 to approximately 250° C. by means of the extruder 16. The partially plasticised plastic material 12 is then introduced into the reactor tank 14 via the entrance opening 30 and is heated there. The plastic material 12 runs upwards in the shape of a screw into the reactor tank 14, whilst being simultaneously gasified. Polyolefin is preferably used as the plastic material. However, other polymers can also be used. It is favourable if anthropogenic plastics are used, in particular plastic materials which are essentially water-free. As the reactor 10 has a tendency towards carbonisation it is generally not well suited to use with organic material.

Should the plastic material 12 be cleaned, the metal bath 26 is brought to a temperature at which the plastic material 12 itself does not decompose, but the contaminants in it do.

REFERENCE NUMERALS LIST

-   10 Reactor -   12 Plastic material -   14 Reactor tank -   16 Extruder -   18 Heating System -   20 Coil -   22 Inner space -   24 Guide apparatus -   26 Metal melt -   28 Gas bubbles -   30 Entrance opening -   32 Column -   34 Recess -   36 Thickening -   38 Inner edge -   40 Pollutant remover -   42 Gas vent -   44 Condenser -   46 Collector -   L Longitudinal axis -   T Temperature -   T_(melt) Melting temperature -   r Radial distance -   A Surface -   D Thickness 

1. A reactor for gasifying and/or cleaning, in particular for depolymerizing, plastic material with (a) a reactor tank for receiving the plastic material, (b) wherein the reactor tank comprises a metal melt, and (c) a heating system for heating the plastic material in the reactor tank, characterized by (d) a guide apparatus arranged in an internal space of the reactor tank for guiding liquefied plastic material in the reactor tank, (e) wherein the guide apparatus is designed to guide the liquefied plastic material on a helical path.
 2. The reactor according to claim 1, wherein the guide apparatus is screw-shaped.
 3. The reactor according to claim 1, wherein the guide apparatus runs upwards with an increasing radial distance, relative to a vertical cross section, so that the liquefied plastic material striking the guide apparatus is guided upwards and to the radial outside.
 4. The reactor according to claim 1, wherein the guide apparatus is constructed from ferromagnetic material in at least some sections.
 5. The reactor according to claim 1, wherein the guide apparatus has recesses which run continuously from bottom to top.
 6. The reactor according to claim 1, wherein the guide apparatus comprises a thickening adjacent to at least one recess.
 7. The reactor according to claim 1, wherein the reactor tank comprises ferroelectric material on at least on the side facing the inner space.
 8. The reactor according to claim 1, wherein it has heat elements in its inner space, which comprise ferromagnetic material.
 9. A process for at least partially decomposing, in particular depolymerizing, and/or cleaning plastic material characterized by the steps: (a) introducing the plastic material into a reactor tank that stretches along a longitudinal axis and comprises a metal melt, (b) heating the plastic material by means of a heating system, (c) guiding the plastic material on a path about the longitudinal axis of the reactor tank by means of a guide apparatus which is arranged in an internal space of the reactor tank.
 10. The process according to claim 9, wherein the plastic material is made predominantly from polyolefin that sets at 23° C. 